1. Field of the Invention
The present invention relates generally to vehicle alternators, and in particular, relates to a magnet retainer ring that is configured to house a plurality of permanent magnets within a rotor.
2. Description of the Related Art
A conventional alternator for a vehicle includes a rotor having a rotor coil that is wound coaxially about a generally cylindrical rotatable shaft. First and second opposed claw poles are mounted onto the shaft on either side of the coil so as to encase the coil, and include a first and second plurality of axially extending fingers, respectively, that intermesh to enclose the outer circumference of the rotor. It is well known that the rotor coil generates magnetic flux when an electric current is passed through it, thereby polarizing the claw pole fingers. In order to reduce the magnetic flux leakage between the claw poles, and thereby increasing overall field magnetic flux and output power, it is known to include a plurality of permanent magnets in the rotor. Such an assembly should be designed to permit the magnet-retainer ring to operate reliably, as the rotor typically rotates up to 21,000 rpm during operation of the vehicle and therefore endures severe vibration, acceleration, and may additionally present a corrosive environment. Additionally, the magnet retention mechanism should be refined so as to facilitate ease of assembly and efficiency of manufacture.
Previously manufactured rotors include a plurality of permanent magnets that are mounted at one side of the claw pole finger onto holding strips by an adhesive. Because the typically brittle magnets are not encapsulated, this arrangement is susceptible to vibrations which could create magnet fragments, thereby causing the rotor to fail. Additionally, prior rotor assemblies may require separate heat resistant elements because air is unable to flow through the assembly. The implementation of heat resistant elements results in increased cost of manufacture.
It is therefore desirable to provide a magnet retaining member that protects the magnets from damage during operation of the rotor, that is robust, and that is efficient and relatively inexpensive to manufacture.
A rotor of a rotating electric machine is provided having a simplified magnet retainer ring that is robust and that protects the magnets from becoming damaged or fragmented during operation of the rotor. Furthermore, the magnet retainer ring is constructed so as to be efficiently mass-produced.
In accordance with a first aspect of the invention, a rotor assembly of a rotating electric machine includes a plurality of magnets disposed therein to reduce the magnetic flux leakage between claw pole fingers and to additionally provide additional magnetic flux through the magnetic circuit, thereby increasing overall field magnetic flux and output power. A magnet retainer ring is provided having a generally annular inner ring that 1) is configured to sit within the adjacent claw pole members and 2) has a sufficiently large inner diameter so as to accommodate a rotor coil therein. The magnet retainer ring includes trapezoidal pockets that extend outwardly therefrom, and that are hingedly connected to the ring. The pockets define cavities that are configured to receive a plurality of permanent magnets therein. In accordance with an alternate embodiment, the magnets are overmolded during manufacturing of the magnet retainer ring, thereby permanently housing the magnets. When the rotor assembly installed, the magnets are generally aligned with, and are disposed radially inward with respect to, a corresponding pole finger.
In accordance with another aspect of the invention, the magnet retainer ring includes a flexible base having notches extending therefrom to permit the magnets to be easily press-fit into the cavities. Because the only side of the magnet that may not be permanently encapsulated by the rotor assembly experiences a compressive force, there is a relatively low risk that the magnets will produce fragments that could cause the rotor to fail.
In accordance with another aspect of the invention, the magnet retainer ring is a unitary piece of molded plastic. Additionally, a user may simply insert the magnets into the cavities with, for example, his or her fingers. Accordingly, the magnet retainer ring may be efficiently mass-produced and easily assembled within a rotor.